Chronic electrical stimulation of the canine retina

An electronic retinal prosthesis is under development to treat retinitis pigmentosa and age-related macular degeneration, two presently incurable diseases of the outer retina. Previous studies have established the feasibility of the retinal prosthesis. The goal of these experiments was to investigate chronic stimulation of the retina. These effects were measured by direct examination of the implant, electrophysiology of the retina, electrically elicited responses, and examination of histology post-implant. Implants were placed in 6 dogs. The implant featured an implantable stimulator and a 4×4 array of 460-micron diameter platinum disks positioned on the retina. 6 dogs were chronically stimulated at 0.05 mC/cm² and 0.1 mC/cm² for up to 60 days (10-12 hours/day). No retinal damage was evident from the stimulus. Some mechanical damage of the retina due to array misalignment was apparent in early implants, but this was minimized with improved surgical technique. Bright flash electroretinograms showed no changes in retinal function comparing pre and post implant recordings. Electrically evoked cortical responses were recorded from 1 dog showing that the functional connection between the retina and the remained. Histological analysis revealed normal retina under the array of 1 dog that had been stimulated for 25 days.